1. Field of the Invention
The present invention relates to a radio communication method and a radio base station that shares a frequency band between radio communication systems whose communication areas spatially partially overlap with each other.
2. Description of the Related Art
In recent years, services of radio communication systems according to a variety of communication schemes are being provided. For example, 3GPP (Third Generation Partnership Project), the standardization organization, defines W-CDMA (Wideband Code Division Multiple Access), HSPA (High Speed Packet Access), LTE (Long Term Evolution) or the like. Furthermore, the IEEE (Institute of Electrical and Electronic Engineers) 802 committee defines wireless LAN (Wi-Fi (registered trademark): Wireless Fidelity) and radio MAN (WiMAX: Worldwide Interoperability for Microwave Access) or the like. Moreover, an XGP (eXtended Global Platform) service, which is the next-generation PHS scheme, has also started.
These communication schemes have different features regarding a frequency band, peak data rate, transmission distance or the like, and a radio communication apparatus is proposed which can communicate with radio communication systems using a plurality of different communication schemes. Furthermore, by causing some communication areas of the plurality of different radio communication systems to overlap with each other and by the radio communication apparatus selecting and connecting a specific radio communication system in the overlapping communication area, it is possible to receive a desired radio communication service.
For example, a large cell (e.g., macro cell) base station and a small cell (e.g., micro cell and/or femto) base station forming cells of different sizes, at least part of which overlaps with each other, may be provided (see FIG. 1). When the same operator operates the large cell base station and the small cell base station, two methods are available; a method of operating the large cell base station and the small cell base station at the same frequency and a method of operating those base stations at different frequencies.
When operating the large cell base station and the small cell base station at the same frequency, interference between the large cell base station and the small cell base station becomes a serious problem. For example, it is assumed that only some users access the small cell base station. In this case, there is a high possibility that a mobile terminal apparatus (UE#A) carrying out communication under the control of the large cell base station may receive strong interference through downlink and/or uplink communication near the small cell base station (see FIG. 2A). Furthermore, there is also a possibility that the small cell base station may receive interference from the mobile terminal apparatus (UE#A) (see FIG. 2D).
In an area adjacent to the large cell base station, a mobile terminal apparatus (UE#B) carrying out communication under the control of the small cell base station may receive strong interference from the large cell base station (see FIG. 2B). Furthermore, the large cell base station may also receive interference from the mobile terminal apparatus (UE#B) (see FIG. 2C).
On the other hand, when the radio communication system including the large cell base station and the radio communication system including the small cell base station are operated at different frequencies, it is necessary to provide a frequency band specific to the small cell base station. In this case, an area which becomes a so-called “white space” extends in an area where fewer small cell base stations are installed (area with a low geographic installation density). This may cause a problem that frequencies cannot be used effectively.
To solve the above-described problem, a method is proposed which controls resource allocation to the large cell base station and the small cell base station when sharing a frequency band between radio communication systems whose communication areas partially overlap with each other (e.g., 3GPP TR25.820 (hereinafter referred to as “Non-Patent Document 1”), Y. Wu et al., “A Novel Spectrum Arrangement Scheme for Femto Cell Deployment in LTE Macro Cells” 2009 IEEE 20th International Symposium on Personal, Indoor and Mobile Radio Communications (hereinafter referred to as “Non-Patent Document 2”), D. Lopez-Perez et al., “OFDMA Femtocells: A roadmap on Interference Avoidance” IEEE Communications Magazine, Volume: 47, Issue: 9 (hereinafter referred to as “Non-Patent Document 3), Z. Bharucha et. al, “Femto-Cell Resource Partitioning” 2009 IEEE GLOBECOM Workshops (hereinafter referred to as “Non-Patent Document 4”)).
However, the method described in Non-Patent Document 1 has a configuration using some resources as shared bands for a macro cell base station and femto cell base station and constantly using some resources for only the macro cell. The method causes a problem that the frequency utilization efficiency deteriorates depending on the radio communication environment.
On the other hand, the method in Non-Patent Document 2 determines based on a received signal whether or not a macro cell terminal is located near a femtocell base station and reports the determination result to a macro cell base station so as to allocate dedicated resources to the macro cell terminal located near the femtocell base station and allocate shared or dedicated resources to other terminals. This makes it possible to avoid interference from the macro terminal to the femtocell base station in uplink communication. However, there is no disclosure regarding avoidance of interference from the femtocell base station or femtocell terminal to communication of the macro cell base station, or dynamic resource allocation to the femtocell base station and macro cell base station.
Furthermore, Non-Patent Document 4 discloses a method whereby a macro cell terminal identifies a femtocell base station which becomes an interference source, reports it to a macro base station and when the macro base station allocates resources to the macro cell terminal, the macro base station prohibits the femtocell base station which becomes the interference source from using resources allocated to the macro cell terminal. However, since the macro cell terminal needs to identify the femtocell base station which becomes the interference source, one problem is that the amount of processing in the macro cell terminal drastically increases and another problem is that when a considerably large number of femtocell base stations exist in the cell of the macro cell base station, the interference source can no longer be identified. A further problem is that the processing load on the network side increases and the amount of radio resources for individual reporting to the femtocell base station increases.